The present invention relates to an improvement in depolymerizing olefin polymers and more specifically the depolymerization of polymers of isobutene.
The polymers of particular interest in the present invention are the lower polymers or oligomers of isobutene. Frequently the polymers are formed unintentionally in the recovery and purification of isobutene monomer. For example, the sulfuric acid extraction of isobutene from hydrocarbon streams usually results in oligomers comprised of principally dimers, trimers and tetramers.
The isobutene monomer may be more valuable compared to the oligomers because of its wide utilization, e.g., polymerization. The lower polymers, oligomers, have found some degree of utilization as gasoline octane improvers, and the dimers are employed as raw materials for detergent intermediates, antioxidants, lube oil additives and the oxo and Koch reactions. Thus a successful depolymerization need not reduce all of the oligomer or oligomers to isobutene, especially if the principal residual oligomer is diisobutene.
In the past isobutene polymers have been depolymerized by heating the polymers in an externally heated tube (thermal degradation) or contacting the heated polymers with various catalysts such as attapulgite clay or silicamagnesia (catalytic degradation).
The present invention relates to the latter general type of depolymerization, using a novel catalyst, which provides the advantages of depolymerization of the various oligomers to high yields of isobutene monomer and high secondary selectivity to diisobutene. Another advantage is the substantial absence of catalyst coking or the formation of high molecular weight non-volatile products. These and other advantages will become obvious from the following description and explanation of the invention.